1. Field of the Invention
The present invention relates to a bidirectional storage device and transfer system; in particular, to a bidirectional storage device and transfer system for transferring wafer.
2. Description of Related Art
Prior art wafer transfer system, such as shown in FIGS. 1 and 2, includes: a front opening unified pod 1a (FOUP), a single rail over-head transport (OHT) 2a, a transport 3a that is placed movably on the single rail OHT 2a, two platforms 4a that are located at the sides of the single rail OHT 2a, and two loading ports respectively connected to the two tool 4a and located at the bottom of the single rail OHT 2a. Thereby, the transport 3a transfers the FOUP la to the predetermined loading port 5a through the single rail OHT 2a. 
However, because the single rail OHT 2a of the prior art wafer transfer system needs to cooperate with the FOUP 1a, therefore only one path may be designed and the path passes through the overhead of the two loading ports 5a in sequence. In other words, the single rail OHT 2a must first pass through one loading port 5a, then pass through the other loading port 5a. Therefore, more time is required when the transport 3a transfers the FOUP 1a to the other loading port 5a. 
Furthermore, because the single rail OHT 2a requires a turnabout section 21a with a fixed radius of turn, therefore the distance D0 is greater between the single rail OHT 2a that extends from the two ends of the turnabout section 21a, and so requires a wider space for operation.